Replacing (and perhaps upgrading) bad capacitors within a speaker system? [closed]

Question

A few months ago the volume of the left speaker of my pair of low-cost audio monitors began slowly diminishing. Every day it seemed to lose a fraction of it's normal operating volume until the speaker became nearly completely silent. Since I bought these speakers in 2010, I noticed that the left speaker tends to run very hot. So, when the speaker began to die out, I assumed that the speakers were poorly designed and weren't built to withstand their own level of heat, and after a certain amount of time they broke. However, I wasn't sure about the cause. I thought it might have been that a solder joint might have weakened and broken or something like that. However, I thought back to an experience that I had before where my PC's video card made a loud crack and upon investigation, some of the capacitors on the PCB had broken open. This was my first experience with bad capacitors.

So, with that in mind, I thought to pop open my left monitor and check around to see if something was visibly wrong. And sure enough, I saw something that looked like two capacitors that had overheated (i think) and vented some of their fluids.

[I can't post my image due to the spam filter]

I'll admit that, while I'm interested in hardware and electrical engineering, my knowledge is much more limited than I would like it to be. I would love to try this repair/upgrade, but I'm worried about messing it up and winding up with a pair of non-working speakers (which, is only slightly worse than a pair of half-working speakers...).

Now, at this point, I've been able to identify a potential cause of the problem. But, I'm not sure what to do about it, or if I can even do anything by myself.

I know that there are places online where I can get replacement capacitors (in this case, it looks like the caps that were used were 4700uF/35v caps). But is this an easy D.I.Y. job for someone who is inexperienced with electronics and soldering, but is willing to learn?

---

Long story short: I think that I need to replace two capacitors inside my speaker system. The caps that were in there (4700uF/35c) broke too quickly for my liking, maybe due to overheating.

Is replacing these capacitors something that is relatively easy for an inexperienced person?

Do I need a special type of soldering iron or can this be done with a cheap hardware store one?

Also, would it be possible to buy replacement capacitors that are stronger/better/durable/heat resistant, instead of simply re-buying the same type?

Should I (or do I have to) replace the bad caps with new ones that are also 4700uF/35v? Or could I/should I replace them with something else? If i can repair and improve these at the same time, I'd like to. I'm not sure if that's possible though, as I don't really understand how capacitors work...

Finally, If I manage to remove the old capacitors, do I have to do something to remove the capacitor fluids that are all over my speaker's PCB? What can I do to clean that and is there anything I should know about that stuff?

Answer 1

You can replace them with pretty much any capacitor that has the exact same rating. It will be relatively easy to replace them, and can be done with any soldering iron that can adjust its temps to under 400*f coupled with solder that has a similar melting point. Preferably you want an iron that is regulated at the tip (not just a dimmer), but for low-power electronics like this that really isn't as much of an issue.

You'll need to desolder the joints, which just consists of heating them until hot enough to pull out of the holes. If you can manage it, put slight tension on the cap while you heat the solder so it will come out as soon as it's hot enough.

When putting the new one in, make sure to apply a light amount of flux to the joint, then put a small amount of solder on the iron, then touch the dab of molten lead to the joint. If all goes well, it will transfer from the iron to the board. After a successful attempt, cut the cap leads as short as possible. Alternatively, if you feel comfortable, pre-cut those leads to protrude about 3-4mm from the back of the board so that the entire lead is encompassed by the new solder.

Here are some recommended supplies:

376* melting point solder
Waterless Tip Cleaner
Aoyue 937+ Digital Soldering Station

Answer 2

Here are some tips about choosing replacement capacitors: First try to locate the brand of the leaking capacitors. It will most likely be printed on the capacitor itself. Search for the name on the Internet and check their reputation. Some brands (like CapXon for example) are known for their leaky and exploding capacitors. There are even sites dedicated to documenting bad capacitor manufacturers like for example badcaps.net forum. If the capacitor is of reputable brand, then you may have a problem in the circuit somewhere else that destroyed the capacitors.

Next the most important characteristics of a capacitor are capacitance, voltage rating, temperature rating, equivalent series resistance, distance between pins and the diameter of pins and the physical size of the capacitor. Another important parameter is lifetime at the rated temperature.

So when you're purchasing capacitors as a replacement for existing part, first step would be to decide if you should use the same model of capacitor as the existing capacitor or to choose another. With same model, you should expect the performance to be just as good as the original, but that may not be very good in some cases. If the manufacturer is of bad reputation, then you should consider getting capacitor made by someone else with better reputation. So when you're choosing replacement capacitor, the first step would be to locate the datasheet of the broken capacitor. Usually on the capacitor there will be a printed marking consisting of several letters and numbers which will tell you which model line the capacitor belongs to and which model in that line the particular capacitor is. In addition to that, you may see line "Low ESR" written somewhere on the capacitor. If it is there, then do remember it.

Now we'll look for the datasheet. In this example, I'll use a CapXon capacitor. It is marked with manufacturer's name and a line which says \$470\mu F 25V\$ Another line says \$ GL105 ^\circ C P1018\$. Armed with that knowledge, we'll go to the CapXon website. Just enter the name of the manufacturer in your favorite search engine and hopefully it will show the website. On their website, under product category-> aluminium electrolytic capacitor we'll find the list of all capacitors. Using the information we have from the capacitor itself, we'll enter the data into the filter. So the working voltage will be the 4-50 range, capacitance range will be in the 120 to 1000, operating temperature will be -25 to 105. Then click search. We'll get a list of capacitor series matching the description and on the list we'll find GL. Note that next to GL it says Low ESR. That's important and that is often found in the datasheet. Clicking on GL, we'll get the datasheet for the series. The procedure is similar for other capacitor manufacturers too and the datasheets also look similar.

Next, in the datasheet we'll find dimensions. The distance between pins on the new capacitor needs to be the same. Other dimensions depend on the area near the capacitor. If you have plenty of space, you can put a bigger capacitor in and if you don't you'll need to find exact match. Next parameter is the impedance. In this example that would be 0.065.

Now we know what the main important characteristics of the capacitor are. After that, we can go to a site of a well-known distributor and look for compatible capacitors. In this example. I'll use digikey.com, but it doesn't really matter, since we're only after a list of compatible capacitors. So in the search box write capacitor, aluminum and it will show a list such as this one. There you'll be able to filter the capacitors by operating temperature (choose larger range if you thing that the device could be overheating), ESR, diameter, lead spacing, height, case type and so on.

Start by filtering with lead spacing first, since that will have to match. In general, you'll be fine picking the higher capacitance, higher voltage and higher temperature range than the capacitor that died had.

Answer 3

Soldering is easy. Pre-solder the leads, add heat then solder then cool it, twist the wires re-solder with bit more added.

Defining the "best cap" all depends if your amp is unipolar or bipolar powered.

Buying caps are easy.

It also depends if you care as much as audiophile purists about capacitors.

Some designs prefer to use polarized aluminium caps with low ESR to support high AC currents and low loss tangent for leakage, adn rated at the highest temp of 105'C rather than 85'C. This is IDEAL when used with automotive DC coupled outputs or cheap unipolar monitor speakers. But if the audio amplifier uses a bipolar PS, you need a non-polarized capacitor.

But if this is a high power bipolar speaker system with a crossover then you may need more expensive caps.

Were these two caps in series with reversed polairity?

In this situation, as one cap gets reverse biased it leaks more and gets warm and acts as a "diode clamp" circuit and bias the other capacitor in the forward direction and visa versa so that AC signals can pass through without exceeding the capacitor reverse voltage spec. But eventually they both leak current and fail from overheating then leak toxic electrolyte. (carcinogen)

I don't know for sure if FW series caps with two in series reversed are tbe best for your application, but it won't harm the speakers or your amplifier so buy extra ones as they good caps and cheap compared to shipping cost.

I know nothing about the power levels of your amplifer or personal use, so I cannot vouch for it's longevity without more details. But the Nichicon FW series is my best advice for now.

See if you can determine if the amp is DC biased out. That makes it easier to use a polarized cap. rather than for the crossover circuit.

I do know electrolytic caps can be operated safely in the reverse direction at 10% of its +ve rated voltage and plastic caps are much lower better in many respects but lower density and more expensive so that values are limited at the high end. At 50% they can pop or fizz.

So I would get the highest temperature rating 105'V vs 85'C and get the highest voltage rating you can find 50V vs 35V and the lowest ESR and loss tangent is also most important. Of course each of these affect cost.

Welcome to (the life of tradeoffs of) Component Engineering. Perhaps one of the audio design engineers can elaborate with their experiences.

Here's a report on microphonics of caps effecting sound quality.